The lungs exist in a delicate balance between toxic oxidants and the protective activities of antioxidant defense systems. An imbalance in this system, either through an increase in oxidants or a dysfunction of the protective antioxidant defense systems, can lead to pathophysiological events in the lung causing pulmonary dysfunction. One type of pulmonary dysfunction in which an increase in oxidants can contribute is respiratory distress syndrome (RDS).
Infantile respiratory distress syndrome is a leading cause of death in the first 28 days of life. Infantile RDS strikes 1 in 100 babies worldwide and about 10 percent die. The syndrome rarely occurs in term infants but is generally associated with immaturity and low-birth weight (under 2 kg). Adult RDS shows similar clinical characteristics and pathophysiology to the infantile disease and is generally managed in an intensive care facility. The adult disease has diverse etiologies, many resulting from lung insults, such as diffuse infections, aspiration of the gastric contents, inhalation of irritants and toxins, and pulmonary edema arising from such sources as narcotic overdose.
RDS is correlated with an absence or dysfunction of the lung surfactant which coats the alveoli of the lungs where gas exchange occurs, and has been associated with oxygen centered free radicals in the lung or lung cavity known as oxidants, such as superoxide radicals, hydroxyl radicals, hydrogen peroxide which can generate hydroxyl radicals, and lipid peroxides, which have been implicated in cellular injury (Heffner, et al., Am. Rev. Respir. Dis. 104: 531-554 1989); (Halliwell, FASEB J. 1: 358-364 1987).
Synthetic lung surfactant of larger polypeptides having antioxidant moieties, have been described in U.S. patent application Ser. No. 07/789,918 filed filed Nov. 4, 1991, which is herein incorporated by reference. However, the present invention provides an effective synthetic lung surfactant having antioxidant properties to shortened peptides of 3-4 amino acids having the ability to inhibit oxidation of susceptible compounds into oxidants. The shortened lung surfactants provide a more efficient and more cost effective means of producing therapeutics. The present novelty of the invention resides in the ability to effectively reduce the peptide to 3-4 amino acids with the retention of surfactant properties and effectively deliver the peptide attached to a covalently bonded antioxidant.
Some synthetic lung surfactant preparations have added therapeutic agents such as Vitamin E to surfactant preparations as a separate component (U.S. Pat. No. 4,765,987; PCT Publication No. WO 90/11768; PCT publication no. WO 90/07469). However, in the present invention the antioxidants are not a separate component but are actually incorporated into a polypeptide. An advantage of incorporating the antioxidant into the polypeptide is that instead of having a three component mixture (lipid, polypeptide and antioxidant), a two component mixture is available. This can be a significant advantage in testing for efficacy for a marketable pharmaceutical where a variety of dosages and formulations must be tested for each component. Additionally, a two component formulation is easier to manufacture.
The polypeptides of the present invention may be used singly in mixtures with lipid or in combination in mixtures of lipid wherein the polypeptide comprises a minor component of the surfactant mixture. The composition of the present invention may be prepared in high purity and in a standardized fashion as it is a defined mixture of synthetic components. Also, the components are not derived from animal sources which minimizes the risk of contamination by viruses and bacteria.
A helical wheel representation of an amphipathic .alpha.-helical ten-residue peptide (for description of the amphipathic .alpha.-helical peptide see McLean, L. R. et al. Biochem., 1991, 30, 31) is used to develop a model for three and four residue peptides. When looking down the barrel of the .alpha.-helix, the side chains of the residues indicate a hydrophobic face and a hydrophilic face on the helix. A four residue peptide represents a single turn of this .alpha.-helix with the required hydrophobic and hydrophilic face present. A three residue peptide represents a constricted turn of the .alpha.-helix with the hydrophobic and hydrophilic face still present.